In the design of pressure switches, a rod slidable within a housing and movable by changes in external fluid pressure operates a plunger of a mechanically operated electrical switch. Resistance of the rod to movement, and hence the pressure at which the switch trips, is adjusted by a spring within the pressure switch that is biased against movement of the rod due to external fluid pressure. Adjustment of the compression on the spring changes the tripping pressure, which for example may be set at 500 psi. Often the interior of the switching housing cannot exceed a certain temperature, but the switch may need to be used in high temperature environments. There is a need for a high temperature operating pressure switch.